The invention relates to a roof tile, and more particularly a roof tile having a watercourse which includes a water stop.
In the production of roof tiles according to the extrusion method onto a strand or extrusion line of abutting subforms of equal length delivered at constant speed is applied a green concrete layer as an endless band, which is shaped on the top side by forming tools corresponding to the surface contour conventional for roof tiles. The continuously applied green concrete layer is subsequently, by means of a cutting tool developed as a blade, cut at each end of each subform in a cutting station, such that each subform carries a single roof tile blank. The roof tile blank on its subform is subsequently cured in a drying chamber and, after it is cured, is provided with a surface coating. Such a method for the production of roof tiles is described in DE 35 22 846 A1.
In order to roof a pitched roof with such roof tiles to make it tight against driving rain, it is necessary that the roof tiles adjacent in a ridge-to-eaves line are placed such that they overlap. The particular length of overlap is herein dependent on the particular slope of the roof, i.e. in the case of a roof with very steep slope the overlap can be less than in the case of a roof with very low slope.
Construction measures have, however, been taken in which the roof tile is provided on its underside at the foot-end margin with foot ribs extending transversely. The subforms known from DE 35 22 846 A1 are, for example, equipped at their transverse margins with recesses, such that the green concrete pressed into these recesses forms suspension flanges at the head-end margin of the roof tile blank, and, at the foot-end margin, forms foot ribs extending transversely. In this way during the roofing the ridge-end roof tile can be hooked with its suspension flanges onto a roof batten and with its foot ribs be placed onto the surface of the roof tile adjacent in the direction of the eaves. Due to the foot ribs, in the region of overlap of the roof tiles a type of labyrinth is therein formed which counteracts the rain water from being driven into the roof.
However, the use of these roof tiles is problematic in the case of roofs having a slope of less than 22°, since, due to the low slope of the roof, a very large overlap length of the roof tiles is required. Between ridge and eaves, consequently, a very large number of parallel roof tile rows must be emplaced. Due to such large requirement of roof tiles and the preparation of a roof batten construction adapted to the number of roof tiles, the material and labor costs are considerably increased. Buildings with very low roof slopes are therefore frequently roofed with large-format, less expensive and lighter roofing materials, such as for example sheet metal or fiber-cement slabs.
A change has therefore taken place toward providing the roof tiles with a water stop on their top side in the region of their head-end margin, which stop prevents heavy rain from being driven into the root. In this way the overlapping of the roof tiles can be markedly decreased, such that the material and labor costs are reduced.
DE 18 12 456 A1 and DE 25 08 551 A1 describe methods suitable for providing the roof tile blanks resting on their subforms with a water stop. In both methods, from a green concrete provided separately, first, a water stop is formed which subsequently is pressed or adhered onto the top side of the roof tile blank in the region of the head-end margin. The water stop is therein implemented relatively wide in order to ensure, on the one hand, sufficient dimensional stability and, on the other hand, a material closure connection over a large area.
However, the roof tiles equipped according to the above methods with a water stop have the disadvantage that, due to the use of different green concretes, between the roof tile and the water stop a weakening joint site is formed, which is susceptible to impact and tends to the development of cracks.
To eliminate this shortcoming, a change was proposed according to GB 664010 toward forming onto the head-end margin of the roof tile blank the water stop during the cutting of the green concrete strand into individual roof tile blanks. Roof tile blank and water stop are therefore comprised of the same green concrete. In this way a good connection between water stop and roof tile can be attained.
To ensure stackability and packagability of the roof tiles, the suspension flanges on the underside of the roof tile located at the top in the stack must, however, be disposed very far apart from the head-end margin of the roof tile, in order to make available sufficient space for the water stop, disposed on the top side and directly at the head-end margin of the subjacent roof tile in the stack.
If the roof tile provided according to GB 664010 with a water stop is compared with the roof tiles depicted in DE 35 22 846, FIGS. 6 and 7, in which the suspension flanges are disposed optimally directly at the head-end margin of the roof tile, it becomes apparent that the roof tiles disclosed in GB 664010, due to the large distance of the suspension flanges from the head-end margin of the roof tile, have a markedly reduced cover length. A large number of parallel roof tile rows is consequently still required.
Considered from production-related aspects, it is, moreover, of disadvantage that for the production of roof tiles with a water stop according to GB 664010 a separate set of subforms is required, since the position of the suspension flanges deviates from the position optimal in conventional roof tiles.